The past decade has seen increasing efforts in detecting and characterising exoplanets by high contrast imaging in the near/mid-infrared, which is the optimal wavelength domain for studying old, cold ...planets. In this work, we present deep AO imaging observations of the nearby Sun-like star \(\epsilon\) Ind A with NaCo (\(L^{\prime}\)) and NEAR (10-12.5 microns) instruments at VLT, in an attempt to directly detect its planetary companion whose presence has been indicated from radial velocity (RV) and astrometric trends. We derive brightness limits from the non-detection of the companion with both instruments, and interpret the corresponding sensitivity in mass based on both cloudy and cloud-free atmospheric and evolutionary models. For an assumed age of 5 Gyr for the system, we get detectable mass limits as low as 4.4 \(M_{\rm J}\) in NaCo \(L^{\prime}\) and 8.2 \(M_{\rm J}\) in NEAR bands at 1.5\(\arcsec\) from the central star. If the age assumed is 1 Gyr, we reach even lower mass limits of 1.7 \(M_{\rm J}\) in NaCo \(L^{\prime}\) and 3.5 \(M_{\rm J}\) in NEAR bands, at the same separation. However, based on the dynamical mass estimate (3.25 \(M_{\rm J}\)) and ephemerides from astrometry and RV, we find that the non-detection of the planet in these observations puts a constraint of 2 Gyr on the lower age limit of the system. NaCo offers the highest sensitivity to the planetary companion in these observations, but the combination with the NEAR wavelength range adds a considerable degree of robustness against uncertainties in the atmospheric models. This underlines the benefits of including a broad set of wavelengths for detection and characterisation of exoplanets in direct imaging studies.
We present the results of a particle simulation studying the local flow of a viscous, self-gravitating disk in Keplerian motion. Our method is based on Wisdom and Tremaine's (
Astron. J.
95.3, ...925–940, 1988) local simulation of planetary rings, but includes self-gravity. We implement a new numerical prescription of interparticle viscosity that formally reduces to Navier-Stokes stresses. Inclusion of hydrodynamic Navier-Stokes-type viscous friction is essential for the system to develop a secular instability for high values of the stability parameter (
Q
> 1). In the framework of a linear perturbation theory wavelength and growth time of the most unstable mode are derived for a “softened” potential that is used in the simulation. The objectives of this paper are twofold: predictions regarding wavelength and growth time of a secular ring instability can be confirmed numerically. Moreover the relative density enhancement in the perturbed regions can be determined in the nonlinear particle simulation; it reaches values twice the unperturbed density. The possible relevance of this mechanism for structuring protoplanetary accretion disks and planetary rings is briefly discussed.
We present a method to correct the chromatic and airmass dependent extinction for N-band spectra taken with the TIMMI2 instrument at the ESO/La Silla observatory. Usually, the target and calibrator ...star have to be observed at similar airmass in order to obtain reliable spectrophotometric fluxes. Our method allows to correct the atmospheric extinction and substantially improves the spectrophotometric flux calibration, when the standard stars were observed at a very different airmass than the targets. Hundreds of standard star measurements in several passbands (N1, N8.9, N10.4, N11.9) were used to derive mid-IR extinction coefficients. We demonstrate that applying our correction of the differential extinction to test data results in a spectrophotometric accuracy up to 2% within the literature flux.
We report the results of mid-IR observations with VISIR at the VLT of 10
ultracool dwarfs members of the nearby Upper Scorpius OB association in four
filters ranging between 8.59 (PAH1) to 12.8 ...$\mu$m (Ne II), and one brown dwarf
with Spitzer between 3.6 and 24 $\mu$m. Seven of our targets are detected in at
least one of the bands, and we derive upper limits on the fluxes of the
remaining 4. These results combined with previous studies from the literature
lead to an improved disk frequency of 50$\pm$12%. This frequency is
significantly higher than that of accretors (16.3%$\pm$6.2%). Only one object
showing mid-IR excess also has H$\alpha$ emission at a level indicating that it
must be accreting. Four of the detected targets are multiple system candidates.
The observed disk frequency for sub-stellar objects in the Upper Scorpius
association is similar to that of stars, consistent with a common formation
scenario. It is also similar to the disk fractions observed in younger
clusters, suggesting that the disk lifetimes might be longer for ultracool
dwarfs than for higher-mass stars.
Young Nearby Loose Associations Torres, Carlos A O; Quast, Germano R; Melo, Claudio H F ...
arXiv.org,
08/2008
Paper, Journal Article
Odprti dostop
A significant population of stars with ages younger than the Pleiades exists in the solar neighborhood. They are grouped in loose young associations, sharing similar kinematical and physical ...properties, but, due to their vicinity to the Sun, they are dispersed in the sky, and hard to identify. Their strong stellar coronal activity, causing enhanced X-ray emission, allows them to be identified as counterparts of X-ray sources. The analysis presented here is based mainly on the SACY project, aimed to survey in a systematic way counterparts of ROSAT all-sky X-ray sources in the Southern Hemisphere for which proper motions are known. We give the definition, main properties, and lists of high-probability members of nine confirmed loose young associations that do not belong directly to the well-known Oph-Sco-Cen complex. The youth and vicinity of many members of these new associations make them ideal targets for follow-up studies, specifically geared towards the understanding of planetary system formation. Searches for very low-mass and brown dwarf companions are ongoing, and it will be promising to search for planetary companions with next generation instruments.
We present preliminary results concerning a survey for triple systems among Pre-Main Sequence (PMS) binaries. Among the 37 systems of our sample, 7 are found to be triple and 6 quadruple. Accounting ...for two additional companions known from other studies, this corresponds to a degree of multiplicity among binaries (number of triples or quadruples divided by the number of systems) of 35 ±10%.
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